Generator



Dec. 11, 1945.

H. Y. FISHER 2,390,877

GENERATOR Filed March 23, 1944 Patented Dec. 11, 1945 asses-2's onnnna'ron liardin Y. Fisher, Hillside, 51., assignor to Nicoud I Mfg. 00., a corporation oi Kllinols application March 23, llldd, Serial No. 527,697

(Cl. 17li--29) 3 Claims.

This invention relates to a generator, and more particularly to agenerator a oted to be operated at widely varying speeds, as ball-25 of a mechanical flashlight.

One feature of this invention is that it provides an improved generator; another feature of this invention is that it provides a small generator particularly designed to have a substantially stable output despite operation at widely varying speeds; another feature is that it provides an improved generator particularly designed for and adapted to be used in a mechanical hand flashlight; and still a further feature of this invention is that limitation of the outputis achieved without the use of moving parts or complicated arrangements. Other features and advantages of this invention will be apparent from the drawing, in which:

Figure 1 is a vertical view, principally in section, of a hand flashlight including the generator embodying this invention; Figure 2 is a transverse vertical sectional view along the line 2-2 of Figure 1; and Figure 3 is a view of the stator portion of the generator.

While the generator which is particularly the subject of this application is shown and described as part of the mechanism of a hand-operated flashlight, because it was designed for that purpose and finds its particular usefulness and ad vantage there, it will beunderstood that the generator includes features which have broader application. A generator of this type might be used in connection with a bicycle, for example, since that field of use also presents problems in providing a stabilized and properly limited electrical output by a generator operated at widely varying speeds.

One of the principal problems in connection with a generator driven at widely varying speeds, of course, is properly to stabilize or limit its output in an inherent and automatic manner, without the use or need of accessories, relays, and the like. However, this problem cannot be considered independently of other generator characteristics, as it is highly undesirable to have a generator with high starting torque or low efliciency. Moreover, in a generator of the permanent magnet type. as that disclosed here, the path traveled by lines of flux must be so arranged that there is no demagnetizing eil'ect upon the magnet which would destroy the usefulness of the generator after a certain'period. The problems presented by these various factors and considerations are, at least; to a certain extent, mutually interdepend cut; and the desired output limiting must be:

Referring now more particularly to Figures 1 and 2, the hand-operated flashlight is shown as comprising a handle portion I 0 and a head II. The head includes a glass or other transparent disc 12, a reflector I3, a lamp l4, and a lamp receiving socket 15, as its principal elements. In

addition, it may provide a'space for the storage of a spare lamp l 5.

The handle portion l0 serves as a housing for the generator and for the ratchet and gearing of the actuating mechanism; and as a mounting means for the pivotally mounted lever N. This lever is pivotally mounted about the pin is and is urged by a spring (not shown) to the position illustrated in dotted lines, being adapted to be moved to the position shown in solid lines by closing of the hand; i. e., operation of the device is eflected by alternately moving the lever 11 between such two positions, the inward stroke being what may be termed the power stroke and the outward stroke the idling stroke. A sector l9 meshes with a pinion 20 which operates through a ratchet mechanism 2| (not shown in detail here,

' since a ratchet or clutch arrangement is conventional in devices of this kind) to provide a unidirectional drive for the gear 22 which operates through a step-up gear arrangoment comprising another pinion 23 and gear 24 to drive the pinion 25 on the shaft of the rotating portion of the genorator.

The generator comprises a stator portion divided into two sections, as will hereafter be more fully described, this stator including the two windings or coils 26 and 21 and laminatlons on which they are mounted. The rotating portion of the generator is in this case the magnet, here shown as comprising a disk 28 of material having the desired magnetic characteristics, as Alnlco, so magnetized as to be provided with two pairs of poles with their magnetic axes perpendicular to each other. IAS is well understood in the art, rotation of this rotor magnet'28 causes lines of force to cut the windings of the coils 26 and 21 and generate electrical voltages therein which result in current outputs when the coils are connected to an appropriate load, as the lamp H. Since no commutating arrangement is used the output of the generator is of the alternating current type,

' at a frequency twice that of the rotation of the rotor magnet28. Two ends of the coil windings,

.. of laminations on which the coils are mounted,

are particularly important; ,and'speciflc dimensions and arrangements will be given for the generator embodying the proportions which I have found to be most effective. Referring now more particularly to Figure 3, it will be seen that the stator portion of the generator comprises two identical units, each consisting of a stack of laminations and a coil. Inasmuch as these are identical, only one unit will be described in detail. Referring now more particularly to the unit shown to the upper left in Figure 3, the core section comprises a plurality .of c-shaped or crescent shaped laminations with an inner substantially semi-circular periphery, the upper lamination of this stack being here identified as 29,

the center portion of each lamination being reduced, as the portion 29a, to provide a coil core on which the coil is wound. The portion of the lamination to each side of the coil is of substantial width, but this width tapers down sharply to quitenarrow tips or end portions here identifled as 29b and 290. The end faces of these end portions 2% and 290 are adjacent but slightly spaced from (although quite close to) the corresponding end faces of the end portions 30b and 300 of the laminations of the other unit, as the laminations identified here as 30. This provides a circular enclosure within which the rotor magnet disk '28 rotates. The spacing between the outer periphery of the rotor magnet and the inner periphery of this enclosure and the spacing between the ends of the confronting core laminations ends and their area are of particular importance in achieving the desired results. The spacing between the rotor magnet and the inner periphery of the enclosure and between the ends of the core laminations, should preferably be from about /1 to 60 of the rotor magnet diameter; and the area of the stack ends, in square inches, should be of the same numerical order. The openings 29d, 29e, 29f, and29g are for small iron rivets staking the laminations together and for mounting screws; and the notch 2971. is present merely to provide clearance for the shaft of the pinion 23 in the compact assembly as shown in Figure 1.

In a particular preferred embodiment of this invention heretofore constructed by me, the four pole rotor magnet disk had an outer diameter of 1.250 inches and was inch thick. The laminations were of .0136 inch thick silica steel, seventeen laminations being used in each stack, the resultant stack thickness being about .232 inch. The diameter of. the circle provided by the internal periphery of the stacks was 1.281 inches, so that there was a clearance of .0155 inch between the magnet and this inner periphery. The air gaps between the confronting ends of the stacks were .016 inch, and the area of the stack ends .01452 square inch each. The portion of each lamination providing the coil core was inch long by inch thick; and the total width of the laminations immediately adjacent the end of this coil core portion was .232 inch. The windings comprised 250 turns each of No. 29 enameled magnet wire giving a total D. C. resistance of 3 ohms. The metal of the magnet disk was first charged to saturation with the poles in the appropriate positions indicated by N and S in Figure 3, then drawn to a somewhat lesser strength producing three volts and .15 ampere through an eighteenohm load at a speed of operation of the generator rotor in the neighbor hood of 2,000 revolutions per minute.

As the speed of operation of the generator increases during the use of the device, the frequency of the current generated increases at the sameratlo, andthis causes a similar increase in A. C. reactance or imp dance in the coils. This is not suilicient, however, to prevent a much wider swin n voltage than isdesirable with consequent burning out of the lamp at high Speeds.

Additional regulation of the output must be achieved; and in this generator it is done by the provision of the small but definite air gap between the closely approaching ends of the two stacks. The air gaps providing a low but definite amount of reluctance results in little flow of magnet flux completely around the rotor core or frame at low or medium generator speeds; but the reluctance of this magnetic path is low enough, because of the close spacing of the ends. that at higher speeds a substantia1 amount of flux traverses both lamination sections and both cores. It is my theory that this flux set up by the current in the coils is to be distinguished from the flux of the permanent magnet, and that it provides a counter-magneto motive effect which increases as the speed of generator operation increases, and thus supplements the increase in im- De ance of the coils and maintains the generator output within the desired limits. This is also the demagnetizing flux, and by providing a path which does not include the permanent magnet rotor, demagnetizing effects upon this rotor are prevented. Moreover, it is my belief that the starting torque is materially reduced because of the fact that little pull-away force is needed to move one of the permanent magnet poles from the end of one lamination stack to the next, be-- cause of the close juxtaposition of the ends of these stacks. Also, both during rotation of the magnet disk, and when it is standing still, the close approach of the lamination ends provides what may be termed a keeper flux path between the poles in what may be termed the side positions, where their flux does not thread the coils, so that this flux does not tend to pass back through the magnet disk itself and demagnetize the disk. Whatever the reasons or the principles underlying the operation of this generator, however, and whether or not the above theories of its operation are entirely correct, it is a fact that a generator closely conforming to the exact specifications and arrangement illustrated and described provides a great improvement and has the desirable features heretofore mentioned.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim: v

1.- An alternating current generator adapted to be operated at widely varying speeds and to provide an approximately constant electrical output, including: a coil element; a permanent magnet element, these elements being relatively movable;

' and means providing a magnetic circuit including said coil but encircling said magnet, this means having spaced ends forming an air gap therein but being of relatively low reluctance, the reluctance being such that substantially no flux traverses said air gap until the output of the generator approaches the desired value, but low enough that there is a substantial quantity of flux traversing said gap when the generator is being driven at a speed at or above that providing the desired output, thespacing betweensaid ends, and between the magnet and the enclosure when expressed in inches, and the area. of each of said ends when expressed in square inches, being ubstantially numerically equal.

2. An alternating current generator adapted to be operated at widely varying speeds and to provide an approximately constant electrical output, including: a pair of C-shaped members of material having high magnetic permeability, these members being arranged with their ends closely adjacent but not abutting so as to form an air gap therebetween; a coil encircling a portion of each of said members; and a permanent magnet rotatable within the enclosure formed by said members, the reluctance of the magnetic path provided by said C-shaped members being such that substantially no flux traverses said air gap until the output of the generator approaches the desired value, but low enough that there is a substantial quantity of flux traversing said gap when the generator is being driven at a speed at or above that providing the desired output.

3. An alternating current generator adapted to be operated at widely varying speeds and to provide an approximately constant electrical output, including: a pair of crescent shaped members of material having high magnetic permeability, these members lying in a plane and .being arranged with their ends closely adjacent but not abutting to forma substantially circular enclosure; a permanent magnet rotatable within but slightly spaced from the inner periphery of said enclosure, said spacing being between one-fiftieth and one-hundredth of the rotor diameter; and a pair of electrically connected coils, each coil encircling a portion at the center of each of said members, the spacing between said ends, and between the magnet and the enclosure when expressed in inches, and the area of each of said ends when expressed in square inches, :being substantially numerically equal.

. HARDIN Y. FISHER. 

